This invention relates to sewing machines and more particularly to program controlled automatic sewing machines.
Sewing machines with a work element or holder for moving a work piece through a predetermined pattern relative to the machine's sewing needle are known. They are particularly useful when the same pattern is stitched repetitively. Zigzag, monogram, bar tack and button hole stitching are familiar examples. The earliest of these automatic sewing machines were complex cam controlled devices in which the entire cam apparatus has to be replaced and time consuming adjustments made whenever it is desired to change a machine from sewing one pattern to another. Even so, certain cam controlled machines, such as those for sewing button holes and tacking, have no capability at all for conversion to other stitch patterns.
More recently, automatic sewing machines have become available in which the work holder is moved according to a sequence of instructions stored in a mechanically controlled element such as a punched paper tape, cards, or a magnetic tape. In such machines the sequence of instructions in the recording medium controls the movement of the work holder during the portion of each needle cycle when the needle is out of the work.
Automatic sewing machines with work holders using paper or magnetic tape or cards to control their movement, however, suffer several disadvantages. First, the tape and card machines move relatively slowly from one location of stored information to the next location. Accordingly, for the machine to work fast enough, a complete instruction must be placed in a single storage location. Further, the complexity of the operation of the sewing machine is limited by the amount of information which can be placed in each such location. A second limitation, mechanical in nature, exists because of the speed of the sewing machine is limited by the speed at which the storage medium can be physically moved from one storage location to the next. Third, a paper or magnetic tape or card reader is relatively costly in comparison to cam controlled machines. Further, though buffer units to enable faster operation are available, they considerably increase the expense of the system.
It is therefore one object of this invention to provide an improved automatic sewing machine in which the speed of movement of the work holder is not limited by mechanical limitations in the instruction storage medium. Other objects include providing an apparatus which controls the movement of the work holder more accurately and with more flexibility than heretofore and which is relatively inexpensive yet reliable. It is also an object to provide an automatic sewing machine which is capable of producing virtually any sewing pattern within the clamp boundaries with stitches of variable length and at needle speeds determined primarily by the maximum stitch size to be sewn. Further, other and additional objects and advantages of the invention will become apparent from the description which follows, the drawings and the appended claims.